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Generics doubt

 
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Hi All,
See the foolowing code below

public class Animal
{
public static void main(String[] args)
{
Animal an=new Animal();
List<Object> lstobj=new ArrayList<Object>();
List<? extends Animal> lstani=new ArrayList<Animal>();
lstani=an.display(lstobj>;
System.out.println(lstani);

}

public <E extends Animal> List <? extends Animal> display(List lst)
{
lst.add(new Object());
return lst;
}

}
class Dog extends Animal
{
}


My doubts is

public <E extends Animal> List <? extends Animal> display(List lst)

In the above method declaration it can accept whatever extends Animal but why is it accepting a Object as argument.


Thanks All
 
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Hi

nik

change your method this

public <E extends Animal10> List <? extends Animal10> display(List<E> lst)
{
lst.add(new Object());
return lst;
}

Check the bold words, you will come to know why is it accepting?

Thanks
Anil Kumar
[ May 14, 2007: Message edited by: anil kumar ]
 
Nik Arora
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change your method this

public <E extends Animal> List <? extends Animal10> display(List<E> lst)
{
lst.add(new Object());
return lst;
}



Hi Anil i changed and tested but i am not understanding the behaviour of the method why it works when its changed. So can you explain me?
 
anil kumar
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Hey

nik

------------------------------------------------------------------------
public <E extends Animal> List <? extends Animal> display(List lst)
-------------------------------------------------------------------------

<E extends Animal>

what does it mean ?

You are saying to the compiler that , the elements in the list are of subtypes of Animal type.

Ok

Up to this point is ok

But you have to say to list also.Which you did not?


display(List lst)// line 1

There is no restriction,that the list must contain the elements which are subtypes of Animal.

ok

if you declare like this

display(List<E> lst)

Then the compiler will check what is <E> here.Which you defined eariler.

i think it is clear

Thanks

Anil Kumar
 
Nik Arora
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Hi Anil,
Look at the below statement

public <E super Animal> List <? super Animal> display(List lst)
-------------------------------------------------------------------------

Why the above statement wont compile?
 
anil kumar
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hey

nik


check this once

click here
[ May 15, 2007: Message edited by: anil kumar ]
 
Nik Arora
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Hi Anil,
I have looked at that document i am not getting
 
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